1. Field of the Invention
The present invention relates to a device using a piezoelectric element including a layered piezoelectric element and a driven member driven by the layered piezoelectric element.
2. Background Art
As shown in FIG. 12, a conventionally known device using a piezoelectric element includes a layered piezoelectric element 100 and a driven member 200 driven by the layered piezoelectric element 100. The driven member 200 is bonded, by means of an adhesive, to one surface 100a of the two end surfaces in the layer stacking direction of the layered piezoelectric element 100 (refer to, for example, Patent document No. 1). The other surface of the end surfaces in the layer stacking direction of the layered piezoelectric element 100 is fixed to, for example, a base 300. The other surface of the end surfaces in the layer stacking direction of the layered piezoelectric element 100 (i.e., the end surface to which the driven member 200 is not bonded) may be a free end surface.
It should be noted that, in the present specification, claims, and drawings (hereinafter may be collectively referred to as “the present specification, etc.”), the term “piezoelectric” encompasses “piezoelectric” and “electrostrictive.” Therefore, for example, the term “piezoelectric element” encompasses both an element having a piezoelectric effect (i.e., a piezoelectric element) and an element having an electrostrictive effect (i.e., an electrostrictive element).
As shown in FIG. 13, the layered piezoelectric element 100 includes a plurality of piezoelectric layers (i.e., layers formed of a piezoelectric material) 101; a plurality of internal electrode layers 102; a plurality of internal electrode layers 103; and a pair of end piezoelectric layers 104. The internal electrode layers 102 are electrically connected to one another. The internal electrode layers 103 are electrically connected to one another. One of the internal electrode layers 102 faces one of the internal electrode layers 103 via one of the piezoelectric layers 101 sandwiched therebetween.
That is, the piezoelectric element 100 is a ceramic layered product in which each of the piezoelectric layers 101 and each of the internal electrode layers (102 and 103) are alternately stacked. Each of the piezoelectric layers 101 is sandwiched between a pair of internal electrode layers 102 and 103 facing each other. A “changing voltage” is applied to each piezoelectric layer 101 through the internal electrode layers 102 and 103 sandwiching the piezoelectric layer 101, and thus a “changing electric field” is applied to the piezoelectric layer 101, whereby the piezoelectric layer 101 expands or contracts in the layer stacking direction. Therefore, a portion of the stacked piezoelectric layers 101, “the portion sandwiched between the internal electrode layers 102 and 103” forms an “active portion KS” (see FIG. 14).
Meanwhile, an electric field cannot be applied to a portion of each piezoelectric layer 101 at which the internal electrode layer 102 does not face the internal electrode layer 103 via the piezoelectric layer 101 (i.e., a portion at which the internal electrode layer 102 and the internal electrode layer 103 do not overlap with each other as viewed in the layer stacking direction, the portion being in the vicinity of each side surface of the piezoelectric element 100). The piezoelectric layer 101 therefore neither expands nor contracts at the portion, and, as shown in FIG. 14, the portion forms a “side inactive portion SF.”
A pair of the end piezoelectric layers 104 are respectively provided (stacked) on the two ends of the layered product including the active portion KS and the side inactive portion SF. Since neither of the end piezoelectric layers 104 is sandwiched between the internal electrode layers 102 and 103, an electric field cannot be applied to the end piezoelectric layer 104. Therefore, the end piezoelectric layers 104 neither expand nor contract, and, as shown in FIG. 14, each of the layers 104 forms an “end inactive portion TF.” It should be noted that the end piezoelectric layer (end inactive portion TF) 104 may be provided (stacked) on only one end of the layered product including the active portion KS and the side inactive portion SF.